By default Events Manager settings has the usage of featured images in events not enabled.
You can start using it as following :
* Go to -> Events -> Settings -> Performance Optimization -> Thumbnails and choose "yes" for "Use WordPress thumbnails?"
* Go to -> Events -> Settings -> Formatting -> Events -> "Default event list format" and insert code like this :
{has_image}#_EVENTIMAGE{100,100}{/has_image}
{no_image}<img src=" - your img url here -"/>{/no_image}<br/>
This should load your default image if there's no featured image for an event, and it should load the featured image that was chosen per event.
Here's an example of featured image usage in events with Events Manager :
For an events list in a widget it's more or less the same :
Copy the above mentioned code right after the existing code in the widget. See here an example of all the text in the widget after that :
https://help.squat.net//featured_images_with_events/example-featured-images-with-events-manager.txt
And a screenshot of an example of events widget with featured images in use :
